Tomography System

ABSTRACT

A measurement system is presented. The measurement system includes a source and a detector located a selected distance from the source with the source and the detector movable about a point, an axis or about a plane located proximate the detector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit ofco-pending U.S. patent application Ser. No. 11/195,463, filed Aug. 2,2005 under 35 U.S.C. §120.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates generally to tomography and totomosynthesis systems and more particularly to a tomography system thatprovides improved three-dimensional breast imaging of tissue.

BACKGROUND OF THE INVENTION

As is known in the art, two techniques for acquiring images of bodysections are tomosynthesis and tomography.

In tomosynthesis, a plurality of images are acquired as a radiationsource traverses a path relative to the object being imaged. Theradiation source emits a radiation signal (typically collimated) whichimpinges upon the object being imaged. At least portions of the emittedradiation signal propagate through the object and are sensed or detectedby a fixed detector located on an opposite side of the object from thesource.

The images acquired by the detector are combined (reconstructed) by asystem of back-projection, error calculation and correction, and forwardprojection repeated one or more iterations until a stopping criteria(including one of iteration count) is reached. It is possible toreconstruct any plane in the object being imaged that is parallel to thedetector. Generally, features of structures outside of the tomosynthesisplane of interest are of reduced intensity do not align precisely whenthey are so combined, which results in a depth-dependent reinforcementof in-plane, and diminution of out-of-plane structures. Theseout-of-plane structures are superimposed into the reconstructed plane,which can degrade the overall reconstructed image quality and results inan image having relatively low depth resolution.

While the above-described tomosynthesis technique has proven useful fordetecting early forms of breast cancer, it is still possible for thedetection of breast cancer to be missed by a physician or radiologistreviewing the data. For example, breast cancer may be missed by beingobscured by radiographically dense, fibroglandular breast tissue orpositioned inadequately outside the imaging volume for example.

The tomosynthesis technique of imaging tissue also generally requiresthat the detector and the object being imaged (e.g. a breast) bemaintained in a stationary or fixed position while the radiation sourceis moved and positioned for obtaining the plurality of images. Thislimits the range over which the source can be moved and thus limits thenumber of different angles of images available to provide the finalreconstructed image of the object.

Similar to tomosynthesis systems described above, tomography systemsalso incorporate a radiation source and a detector. In contrast totomosynthesis systems, tomography systems move both the radiation sourceand the detector mutually about the object being imaged.

In a tomography system, a plurality of images are acquired as acollimated radiation source traverses a path relative to the objectbeing imaged. The radiation source emits a radiation signal whichimpinges upon the object being imaged. At least portions of the emittedradiation signal propagate through the object and are sensed or by adetector or detectors located on an opposite side of the object from thesource. As mentioned above, in a tomography system, both the radiationsource and the detector traverse a path about the object being imagedwhile the object itself is maintained in a stationary position. In oneprior art scheme, the source and detector are translated back and forthand at the end of each translation the source and detector areincremented rotationally to maintain a fixed spatial relationship.Signals corresponding to detected density variations are fed into acomputer which, when information from the whole scan is complete,produces data representative of density variations in a plane which istransverse to the translation direction through which the source anddetector are moved. An image can then be constructed from the data.

One drawback associated with such tomography systems when applied tocertain imaging problems such as breast imaging is that the mostdesirable source and/or detector path can physically intersect with thebody or organ being imaged (e.g. a breast). This is due, in part,because the location of the point or axis about which the radiationsource and detector move is typically located proximate the object beingimaged. Another drawback associated with tomography systems is that tocompensate for the limited movement of the system about a pathsurrounding the object being imaged, the source provides a larger areaof radiation which can result in radiating structures that are not ofinterest. For example, when it is desired to perform breast imaging, itmay be necessary to also expose the chest, shoulder and heart/lungs ofthe person to radiation in order to provide sufficient data toaccomplish the breast tomography.

It would, therefore, be desirable to provide a tomography system thatallows imaging of an entire object without having source, detector orsupport structures intersect with the object or body of the subjectbeing imaged. It would also be desirable to provide a system whichreduces the amount of radiation directed toward structures not beingimaged. It would be further desirable to provide a breast imaging systemin which a source and detector are able to move over a relatively widerange of angles to allow a clinically useful set of measurements to bemade.

SUMMARY OF THE INVENTION

In accordance with the present invention, a measurement system ispresented. The measurement system includes a movable radiation source, amovable radiation detector located a set distance from the source withthe source and detector both being moveable about a point, an axis or aplane located proximate the detector. The source and detector move inunison to maintain a desired spatial relationship which allowscollection of tomographic data. The object being imaged is maintained ina fixed position while the source and the detector are movable about thepoint located proximate the detector. In one embodiment, the point islocated at or below the detector to permit movement of the detector andany detector support structure without intersecting with any portion ofan object being measure and without intersecting with any portion of anystructure associated with the object being measured. In anotherembodiment, the point is located in a plane which is coincident with aplane defined by a first surface of the detector. In still anotherembodiment, the point is located on an edge of the detector. In stillanother embodiment, the point is provided as a pivot axis disposedproximate an upper or lower surface of the detector. In yet anotherembodiment, the point is provided as pivot point disposed proximate anedge or a surface of the detector. In short, the point can be providedat any location proximate the detector which allows the detector and anyassociated detector support structure to move without intersecting withthe object being measured or any structure associated with the objectbeing measured. The source and detector can move along a circular-shapedpath, an elliptically-shaped path or a random polygonal-shaped path.Depending upon the particular path shape along which the source anddetector move, a particular location proximate the detector about whichmovement of the source and detector occurs can be selected. The pointabout which movement of the source and detector occurs can be providedas a pivot point, an axis or a plane. In one embodiment, the point isprovided as an axis of rotation proximate the detector and the sourceand detector are coupled together via a support arm which moves(rotates) the source and detector in unison about the axis of rotation.

By spacing the radiation source a set distance from the detector andallowing both the detector and the source to move about a point locatedproximate the detector, the measurement system can provide imagingmeasurements of an entire object without intersecting with the any partof the object being imaged or other structures associated with theobject being imaged. Thus, the source and detector can traverse arelatively wide range of angles. Since the source and detector cantraverse a relatively wide range of angles, a source which emits aradiation beam having a relatively narrow beamwidth and/or beamshape canbe used. By using a source which emits a radiation signal having arelatively narrow beamwidth and/or beamshape, a system which reduces theamount of radiation directed toward structures not being imaged isprovided.

In a breast imaging system, utilization of a separated source anddetector which are movable about a point located proximate the detectorin a synchronized and tailored source-detector motion results in asystem in which the source and detector can move without intersecting orinterfering with a person's body. Thus, the source and detector cantraverse a range of angles which is wider than a range of anglesachievable with prior art systems. By moving the point about which thesource and detector move to a location proximate the detector, it ispossible to move the detector high into the axilla region of a person'sbody and also to cover upper abdominal regions of the person's body.This results in the system being able to provide an improved mediallateral oblique projection (MLO projection).

Since the source and detector can be moved to positions not possible toreach with prior art systems, the system can measure data which can notbe measured with prior art systems. This can result in a more clinicallyuseful set of measurements. By measuring additional data not measurableby prior art systems, a breast imaging system which incorporates thefeatures described hereinabove is able to provide more detailed andcomplete imaging than prior art breast imaging systems.

Furthermore, since the source has a wider range of travel, the systemcan utilize a source which provides a radiation beam having a cone shapeand a beamshape selected to lessen the amount of radiation impingingupon structures that are not of interest. For example, in breast imagingapplications, it is possible to lessen the amount of radiation whichimpinges upon a person's chest, shoulder, heart and lungs.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the inventionitself, may be more fully understood from the following description ofthe drawings in which:

FIG. 1 is a block diagram of a prior art system for breasttomosynthesis;

FIG. 2 is a block diagram of a prior art system for breast tomography;and

FIGS. 3 and 3A is a block diagram of a first embodiment of a limitedangle conebeam breast tomography system.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a prior art tomosynthesis system 2 is shown.This system is similar to one described in U.S. Pat. No. 5,872,828 toNiklason et al. and assigned to the assignee of the present application.The system 2 includes a radiation source 4 attached to a movable arm 6.Movable arm 6 pivots about an axis or pivot point 8, located between thesource 2 and an object 10 being imaged (e.g. a breast). A fixed arm 12has a first end attached to a radiation detector 14 and a second endattached to the movable arm 6 at the pivot point 8. The object beingimaged 10 (e.g., a human breast) is disposed abutting the detector 14.Typically the object 10 being imaged is compressed against the detector14.

In use, the source 4 is rotated between the source position denoted Aand the source position denoted B. The source 4 provides radiation tothe detector 3 while moving along the arc 16 between the two positionsA, B shown in FIG. 1. The detector 14 remains stationary. From theinformation collected by detector 14, a final synthesized representationof the X-ray absorption of the object 10 is produced as is generallyknown.

Referring now to FIG. 2, a system for performing cone beam volume CTbreast imaging 20 includes a gantry frame 22 on which a cone-beamradiation source 24 and a digital area detector 26 are mounted. Apatient P rests on an ergonomically designed table 28 having a hole (ortwo holes) provided therein to allow one breast B (or two breasts) toextend through the table 28 into a breast holder having an inner portion30 a and an outer portion 30 b. In this configuration the gantry frame22 surrounds the breast B. Thus, the entire breast B can be exposed tothe cone beam provided by the source 24.

The gantry frame is rotatable around an axis 32 which is substantiallycentered in the breast B. Thus, the radiation source 24 and the detector26 move about axis 32 in unison in a circular orbit around the breastwhile the breast remains in the path of the cone-shape radiation beamemitted by the source 24. The system shown in FIG. 2 is similar to thetype described in U.S. Pat. No. 6,480,565 to Ning and assigned to theUniversity of Rochester.

Referring now to FIGS. 3 and 3A in which like elements are providedhaving like reference designations, a breast tomography system 100includes a source 110 (e.g. an x-ray source) and a detector 120.Surfaces of the source and detector are spaced from each other by adistance which does not change during operation of the tomography system100. The detector is here shown as a digital planar detector althoughother detectors known to those of ordinary skill in the art and havingeither flat or curved surface, may of course also be used. It should beappreciated that only the source, detector and mounting arms are shownin FIGS. 3 and 3A and that for clarity and ease of description, otherparts of the breast tomography system are not shown in FIGS. 3 and 3A.

In the exemplary embodiment of FIG. 3, the source 110 and detector 120are coupled to first and second opposing ends of a support arm 140. Anobject to be imaged (e.g. breast 160) is disposed in a support 170 whichis decoupled from the source 110, detector 120 and arm 140, such thatthe support 170 (and therefore the object 160 held in support 170) donot move during movement of the source 110, detector 120 and arm 140. Agrid 180 coupled to a top surface of the detector 120 rejects scatterwhich can occur when the source 110 provides a radiation signal.

The arm 140 (and thus the source and detector coupled to the arm 140)moves about a point 130 located proximate the detector 120. In theexemplary embodiment of FIGS. 3 and 3A, point 130 lies in a plane inwhich the detector 120 lies. As the arm 140 moves, the source 110,detector 120 and arm 140 move through a path (e.g. an arc-shaped path)to the positions shown in FIG. 3A. Throughout the movement betweenpositions, the detector 120 maintains a spatial relationship with thesource 110 consistent with breast tomography techniques.

In operation of the tomography system 100, the radiation source 110emits a beam of radiation toward the detector 120 and the source anddetector pivot about the point 130. Throughout this motion, the breast160 and the detector 120 are disposed in the path of the radiationemitted by the source 110 and the source 110 and detector 120 maintain aknown spatial relationship in accordance with conventional breasttomography techniques. The detector 120 detects the presence of anyradiation which passes through the breast 160 and reaches the detector120.

In the case where the system 100 is used to perform breast tomography, aperson is positioned as shown in FIGS. 3 and 3A and the breast beingimaged (i.e. breast 160 in FIGS. 3 and 3A) is placed and compressedbetween compression plates 170 a, 170 b. It should be appreciated thatthe breast may be supported or held in some other manner rather than viathe compression plates 170 a, 170 b. Regardless of how the breast issupported or held, the source 110 and detector 120 move to measure dataover a range of angles which is wider than possible with prior artbreast imaging techniques utilized with a person in the standingposition. The data will later be used to provide images of the breast.

Since the point 130 about which the source 110 and detector 120 moves isphysically located proximate the detector 120 and/or in a plane of thedetector 120, neither the source 110, nor the detector 120, nor the arm140 interfere with or intersect with the body during movement of the arm140, the source 110 and the detector 120. Thus, it is possible to obtainimages over a wide range of angles without requiring the person whosebreast is being image to lie down.

This is in contrast to some prior art breast imaging systems in which ifthe torso of the person is adjacent a portion of a support arm, thedetector and/or arm of the system will eventually interfere with a bodypart (i.e. the source and/or detector will physically intersect with abody part of the person) thus interfering with the motion of the systemand thus limiting the range of angles over which the, detector and/orarm of the system can be moved.

Since in accordance with the present invention the source 110 anddetector 120 can be moved to positions not possible with prior artsystems, the system 100 can provide data which cannot be provided withprior art systems. Thus, the system 100 is able to provide more detailedimaging than prior art systems.

Furthermore, since the source 110 can traverse a range of angles whichis wider than the range available in prior art systems, the source 110can utilize a radiation beam having a cone shape which has a beamwidthand/or beamshape which is narrow compared with the beamwidth and/orbeamshape of cone-shaped beams used in prior art systems. This allowsuse of a radiation beam which lessens the amount of radiation whichimpinges upon structures that are not of interest. In breast imaging,for example, it is possible to lessen the amount of radiation whichimpinges upon a person's chest, shoulder, heart and lungs and it is alsopossible to lessen the amount of radiation which “spills over” thedetector 120.

Moreover, the fixed relationship of the source 110 to the detector 120permits the use of grid 180 that provides grid-based scatter rejectionand therefore a higher contrast resultant image.

A benefit which results from placing the point about which the sourceand detector move in or proximate a plane in which the detector 120 liesis that when the present system is used for breast tomography, thesystem allows increased measurements of the breast-to-chest area whichis not possible with prior art tomography systems. This can result inthe system being able to provide improved medial lateral obliqueprojections (MLO projections).

The above arrangement thus permits three-dimensional imaging of tissuesuch as a human breast, using a specific motion of the source 110 anddetector 120 while holding the subject tissue (e.g. breast 160)immobilized.

It should be appreciated that alternate embodiments of the tomographysystem 100 of the present invention are also known. For example,although FIGS. 3 and 3A show the point about which the source anddetector lies to be an axis in a plane of the detector, the point 130may correspond to a pivot point, or a plane rather than an axis. Thusreferences made herein to a point about which the source and detectormove are not limited to a specific point but rather are intended toinclude any point implemented as a pivot point, an axis, a plane or anyother structures. Also the point may be located in other positions. Inparticular, the point about which the source and detector move may belocated coincident with, above or below a plane in which a surface ofthe detector lies. The point about which the source and detector movemay correspond to a pivot point or an axis or a plane which ishorizontally displaced from the junction of the detector 120 and arm140. In some embodiments it may be possible to locate the point slightlyabove a plane in which the detector lies. It should, however, beappreciated that in the case where the point is above a plane in whichthe detector lies, the point must be located proximate the detector suchthat no structure interferes or intersects with a person duringoperation of the system. That is to say, the point about which source110 and detector 120 move should be selected such that the source anddetector are able to pivot or otherwise move freely (e.g. rotate)without interfering with (e.g. physically contacting) a subject orpatient. The location of all the pivot points/axis provide for a systemthat does not interfere with or intersect with the body during traversalof the source and detector during the process of generating tomographicbreast images.

It should also be appreciated that in some embodiments the source andthe detector may be independent of one another while still moving aboutthe same point. Thus, rather than the source and detector being coupledtogether via a physical structure (e.g. by support arm 140 in FIGS. 3and 3A) such that they must move in unison, the source 110 and detector120 can be movable independently from another and their movements arecoordinated such that they move in synchronization about the same pointin order to maintain a fixed distance and spatial relationship betweeneach other.

A measurement system has been described. The measurement system includesa movable radiation source, a movable radiation detector located aselected distance from the radiation source with the source and thedetector movable about a point, an axis or a plane located proximate thedetector. By providing a configuration wherein the source and thedetector are movable about a point, an axis or plane proximate thedetector, the system does not interfere with the subject or requireirradiation of body structures that are not of interest and at the sametime enables a set of measurements to be made which may be moreclinically useful than measurements enabled by prior art systems.

Having described preferred embodiments of the invention it will nowbecome apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts may be used. Accordingly, it issubmitted that that the invention should not be limited to the describedembodiments but rather should be limited only by the spirit and scope ofthe appended claims.

1. A measurement system comprising: a detector movable about a selectedpoint located proximate a plane in which the detector lies which thepoint corresponding to one of: a pivot point, an axis or a plane; asource disposed a predetermined distance from said detector and arrangeto emit a signal toward said detector with the source movable about thesame point as the detector and with the source and detector adapted tomaintain a spatial relationship which allows collection of tomographicdata.
 2. The system of claim 1 further comprising a support arm coupledto said source and said detector in wherein said arm is movable aboutthe selected point.
 3. The system of claim 1 wherein said source andsaid detector are coupled such that movement of said source results in acorresponding movement of said detector.
 4. The system of claim 1further comprising a support element disposed to hold an object to beimaged in a fixed position.
 5. The system of claim 4 wherein saidsupport element comprises: a first plate; and a second plate spaced apredetermined distance from and generally parallel to said first plate,and wherein the object to be imaged is supported between said firstplate and said second plate.
 6. The system of claim 1 wherein saiddetector and said source are coupled via a control system such thatmovement of a first one of said source and said detector results in acorresponding movement of a second one of said source and said detectorto maintain the source and detection in a spatial relationship whichallows collection of tomographic data.
 7. A breast tomography systemcomprising: a detector movable about a selected point located proximatea plane in which the detector lies which the point corresponding to oneof: a pivot point, an axis or a plane; a source disposed a predetermineddistance from said detector and arrange to emit a signal toward saiddetector with the source movable about the same point as the detectorand with the source and detector adapted to maintain a spatialrelationship which allows collection of tomographic data. A supportelement disposed between said source and said detector.
 8. The system ofclaim 7 wherein the point corresponds to an axis about which the sourceand detector move and wherein the location of the axis is selected fromthe group consisting of: a location coincident with said detector; alocation below said detector and a location proximate to and above saiddetector.
 9. The system of claim 8 wherein movement of said source andmovement of said detector are synchronized to maintain approximately asame distance between said source and said detector.
 10. The system ofclaim 7 wherein said support element comprises: a first plate; and asecond plate spaced a predetermined distance from and generally parallelto said first plate, with the first and second plates adapted to supporta breast.
 11. The system of claim 7 further comprising a support armhaving a first end coupled to said source and a second end coupled tosaid detector.
 12. The system of claim 11 wherein said support arm isprovided having a generally U-shape.
 13. The system of claim 12 whereinsaid source comprises an X-ray source.
 14. The system of claim 13wherein said detector comprises an X-ray detector.